Liquid crystal projector

ABSTRACT

A liquid crystal projector, having a configuration in which an exhaust fan is arranged adjacently to a projection lens at an angle to the optical axis of the projection lens, a configuration including a plurality of tilted wind-directing plates, a configuration in which the arrangement of a first reflection mirror, a first lens array, a light source and the exhaust fan is substantially parallel and adjacent to the arrangement of the projection lens, a dichroic prism and a second dichroic mirror, and/or a configuration in which the lens array has the incident surface thereof made of a concave lens.

CONTINUATION STATEMENT

This application is a continuation of U.S. application Ser. No.08/959,433, filed Oct. 28, 1997, now U.S. Pat. No. 6,065,838.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal projector using atransmission liquid crystal panel, or more in particular to (1) a liquidcrystal projector for projecting the illumination light from a lightsource on a liquid crystal panel, and projecting an image of the liquidcrystal panel on a screen through a projection lens. The invention alsorelates to (2) a liquid crystal projector in which the illuminationlight from a light source is split into three colors of R, G and B by adichroic mirror and irradiated on three liquid crystal panels, images onthe three liquid crystal panels are synthesized in color through adichroic prism and a synthesized image is projected on a screen througha projection lens. Further, the invention relates to (3) a liquidcrystal projector in which the illumination light from a light source isirradiated on a liquid crystal panel through a reflector, a first lensarray and a second lens array so that the light emitted from the liquidcrystal panel is projected on a screen by a projection lens.

A conventional liquid crystal projector using a transmission liquidcrystal of this type is known, as described in JP-A-63-216026, forexample, which comprises a light source (corresponding to 21), a firstreflection mirror (corresponding to 23), a first dichroic mirror(corresponding to 26), a second reflection mirror (corresponding to 30),a second dichroic mirror (corresponding to 27), a third reflectionmirror (corresponding to 28), a fourth reflection mirror (correspondingto 29), a first transmission liquid crystal panel (corresponding to 33),a second transmission liquid crystal panel (corresponding to 39), athird transmission liquid crystal panel (corresponding to 45), adichroic prism (corresponding to 49) and a projection lens(corresponding to 50), wherein the illumination light from the lightsource is irradiated on the first dichroic mirror through the firstreflection mirror, the first emitted light split in color by the firstdichroic mirror is irradiated on the first liquid crystal panel throughthe second reflection mirror, the second emitted light split in color bythe first dichroic mirror is irradiated on the second dichroic mirror,the first emitted light split in color by the second dichroic mirror isirradiated on the second liquid crystal panel, the second emitted lightsplit in color by the second dichroic mirror is irradiated on the thirdliquid crystal panel through the third reflection mirror and the fourthreflection mirror, the transmitted light from the first liquid crystalpanel, the transmitted light from the second liquid crystal panel andthe transmitted light from the third liquid crystal panel aresynthesized in color by the dichroic prism, and the emitted light thussynthesized in color is projected on the screen by the projection lens.

Another conventional liquid crystal projector is known, as disclosed inJP-A-3-10218, comprising an exhaust fan (corresponding to 15, 27) forcooling a light source.

As disclosed in “High-Efficiency Illumination Optical System for LiquidCrystal Projector Using Deformed Open Lens Array”, 22Fa06 of OpticalFederation Symposium, Hamamatsu '94, pp.135-136, JAPAN OPTICS '94,sponsored by the Japan Optical Society (Application PhysicsAssociation), for example, a liquid crystal projector is known,comprising a light source including a metal halide lamp and a parabolicmirror, a UV-IR cut filter, a first lens array and a second lens array.

A liquid crystal projector configured of a combination of theabove-mentioned three conventional liquid crystal projectors alreadyfinds applications. The prior art will be described below with referenceto the drawings.

FIG. 9 is a diagram showing an optical system of a liquid crystalprojector comprising a combination of the above-mentioned configurationsof the conventional liquid crystal projectors.

The illumination light 51 from a metal halide lamp 50 constituting alight source enters a lamp reflector 52 of a parabolic mirror, a UV-IRcut filter 53, a first lens array 54, a cold mirror 55 constituting afirst reflection mirror, a second lens array 56, and a first dichroicmirror 57 for transmitting the R color light and reflecting the G and Bcolor light, so that the R color light 58 is transmitted and the G and Rcolor light 59 are reflected. The R color light 58 is reflected on anincreased reflection aluminum mirror 60 constituting a second reflectionmirror, and enters a R color light liquid crystal panel 63 constitutinga first transmission liquid crystal panel through a condenser lens 61and a polarizing plate 62. The G and B color light 59 enter a seconddichroic mirror 64 which reflects the G color light and transmits the Bcolor light, so that the G color light 65 is reflected and the B colorlight 66 is transmitted. The G color light 65 enters a G color lightliquid crystal panel 69 making up a second transmission liquid crystalpanel through a condenser lens 67 and a polarizing plate 68. The B colorlight 66, on the other hand, enters a B color light liquid crystal panel76 making up a third transmission liquid crystal panel through a relaylens 70, an increased reflection aluminum mirror 71 making up a thirdreflection mirror, a relay lens 72, an increased reflection aluminummirror 73 making up a fourth reflection mirror, a condenser lens 74 anda polarizing plate 75.

The R transmitted light 77 from the liquid crystal panel 63, the Gtransmitted light 78 from the liquid crystal panel 69 and the Btransmitted light 79 from the liquid crystal panel 76 are synthesized incolor by a dichroic prism 80. The emitted light 81 thus synthesized incolor is projected on a screen (not shown) by a projection lens 82.

In order to prevent the heat generated by the high-temperature lightsource from having an effect on the component parts other than the lightsource, an exhaust fan 83 for cooling the light source is arranged inthe neighborhood of the metal halide lamp 50 and the lamp reflector 52thereby to exhaust the hot air 84 out of the housing (not shown) of theliquid crystal projector.

The liquid crystal projector having this configuration can produce abright, large image on the screen while cooling the high-temperaturelight source. Also, the first lens array 54 and the second lens array 56configured as an optical integrator can irradiate a uniform illuminationlight on the liquid crystal panels 63, 69, 76, thus producing a bright,large image on the screen with a uniform peripheral illuminance. In theconventional liquid crystal projector of this configuration, however,has the problem that the hot air 84 exhausted by the exhaust fan 83often flows toward the viewers located in the neighborhood of the liquidcrystal projector and thus gives the feeling of discomfort to theviewers. Also, the liquid crystal projector is sometimes used in thevicinity of the video equipment such as the personal computer liable tosuccumb to heat easily. In such a case, such video equipment is requiredto be located at a position not exposed to the hot air. Further, inorder to efficiently exhaust the heat generated from the light source,care must be exercised not to place any object constituting a stumblingblock to the exhaustion in a path of the hot air, thereby posing theproblem of operating inconveniences.

On the other hand, JP-A-5-59424 (UM) proposes a configuration in whichan exhaust fan for cooling a light source is arranged in the same planeas the front cylinder section of a projection lens so that the light isprojected in the same direction as the hot air is exhausted. In thisconfiguration, the hot air exhausted from the exhaust fan is preventedfrom flowing toward the viewers located in the neighborhood of theliquid crystal projector. The viewers thus feel no inconvenience, nor isit necessary to take care not to arrange the equipment easily affectedby heat in the neighborhood of the liquid crystal projector or to placean object constituting a stumbling block to the exhaustion in a path ofthe hot air. It is thus possible to obtain a liquid crystal projectorconvenient to use. Nevertheless, this configuration fails to take intoconsideration the fact that the hot air exhausted from the exhaust fanmay flow into the projected light from the projection lens and causefluctuations of the image projected on the screen. Also, no care istaken about a configuration of wind-directing plates to assure anefficient exhaustion of the hot air. Further, no special considerationis taken about the configuration of the optical system including thefirst lens array and the second lens array.

Furthermore, in the conventional liquid crystal projector having theabove-mentioned configuration, the reflector 52 is a parabolic mirrorand therefore parallel light rays enter the first lens array 54, therebyleading to the disadvantage that the first lens array 54, the coldmirror 55, the second lens array 56 and the dichroic mirror 57 increasein size. The increased size of the second lens array 56 results inanother disadvantage that the light utilization rate of a liquid crystalpanel with micro-lenses, if employed, cannot be improved. The reason whythe use of a liquid crystal panel with micro-lenses deteriorates thelight utilization rate will be described with reference to FIGS. 10, 11,12. FIG. 10 is a sectional view of a liquid crystal panel 85 withmicro-lenses. Even when completely parallel-light rays 86 are assumed toenter the liquid crystal panel 85, these light rays 86 emit from theliquid crystal panel as divergent light rays 88 at an angle e under theeffect of the micro-lenses 87. Since the divergent light rays 88 passthrough a pixel aperture 90 without being interrupted by a black matrix89, however, the effective vignetting factor of the liquid crystal panelis improved for a higher light utilization rate. FIG. 11 is a diagramshowing light rays from the second lens array 56 to a projection lensaperture 92 designed for a liquid crystal panel 91 without anymicro-lenses. The incident angle f and the outgoing angle g of theliquid crystal panel 91 are designed to be equal to each other. FIG. 12is a diagram showing light rays from the second lens array 56 to theprojection lens aperture 92 for a liquid crystal panel 85 withmicro-lenses. As apparent in comparison with FIG. 11, the liquid crystalpanel with micro-lenses as shown in FIG. 12 has the outgoing angle g ofthe liquid crystal panel 85 increased by an amount equivalent to thedivergent angle e. Even when the effective vignetting factor is improvedby the micro-lenses 87, therefore, the eclipse developed at theprojection lens aperture 92 prevents the light utilization rate frombeing improved.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above-mentionedproblems of the prior art and to provide an easy-to-operate liquidcrystal projector, in which the hot air exhausted from the exhaust fanis prevented from flowing toward the viewers located in the neighborhoodof the liquid crystal projector, thus eliminating the feeling ofdiscomfort to the viewers, in which it is not necessary to take care notto arrange an equipment easily succumbing to heat in the vicinity of theliquid crystal projector, in which no consideration is required not toplace any object constituting a stumbling block to the exhaustion of thehot air in the path thereof, and in which the hot air exhausted from theexhaust fan is prevented from flowing into the projected light from theprojection lens and fluctuating the image on the screen, while at thesame time improving the exhaustion efficiency of the hot air. Anotherobject of the invention is to provide a technique for improving thelight utilization rate sufficiently even when a liquid crystal panelwith micro-lenses is employed.

In order to achieve the above-mentioned objects, according to thepresent invention, there is provided a liquid crystal projector and atechnique related thereto, in which

(1) an exhaust fan is arranged adjacently to a projection lens andtilted in such a manner that the exhaust air from the exhaust fan flowsfar from the projected light of the projection lens,

(2) the exhaust fan is arranged adjacently to the projection lens, aplurality of wind-directing plates are arranged and tilted in such amanner that the exhaust air from the exhaust fan flows far from theprojected light of the projection lens and that the tilt angle of thewind-directing plate near to the projection lens is larger than that ofthe wind-directing plate far from the projection lens,

(3) a first reflection mirror, a second lens array, a first dichroicmirror, a second dichroic mirror and a third reflection mirror arearranged in that order, and the arrangement of a first lens array, alight source and the exhaust fan is substantially parallel and adjacentto the arrangement of the projection lens, a dichroic prism and thesecond dichroic mirror, and

(4) a reflector is made of an ellipsoidal mirror, and a concave lens isinterposed between the reflector and the second lens array.

The above-mentioned configuration can easily achieve the objects of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an optical system of a liquid crystalprojector according to a first embodiment of the invention.

FIG. 2 is a graph showing the spectral reflectance characteristic of anincreased reflection silver mirror.

FIG. 3 is a graph showing the spectral transmittance of a cold mirror.

FIG. 4 is a top plan view of an optical system of a liquid crystalprojector according to a second embodiment of the invention.

FIG. 5 is a top plan view of an optical system of a liquid crystalprojector according to a third embodiment of the invention.

FIG. 6 is a diagram showing light rays from a second lens array 4 to aprojection lens aperture 92.

FIG. 7 is a top plan view of an optical system of a liquid crystalprojector according to a fourth embodiment of the invention.

FIG. 8 is a top plan view of an optical system of a liquid crystalprojector according to a fifth embodiment of the invention.

FIG. 9 is a top plan view of an optical system of a conventional liquidcrystal projector.

FIG. 10 is a sectional view of a liquid crystal panel with micro-lenses.

FIG. 11 is a diagram showing light rays from the second lens array 4 tothe projection lens aperture 92 for a conventional liquid crystal panelwithout any micro-lenses.

FIG. 12 is a diagram showing light rays from the second lens array 4 tothe projection lens aperture 92 for a conventional liquid crystal panelwith micro-lenses.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments will be explained below with reference to the accompanyingdrawings.

FIG. 1 is a top plan view of an optical system of a liquid crystalprojector according to a first embodiment of the invention.

The illumination light 2 from a metal halide lamp 1 enters a first lensarray 4 through a lamp reflector 3 of an ellipsoidal mirror. A lampreflector 5 of a spherical mirror is inserted for the purpose of reusingthe illumination light 6 not used conventionally by returning it to themetal halide lamp 1.

The first lens array 4 has an incident surface 7 of a concave lens andhas the function of converting the convergent light rays 8 from the lampreflector 3 of the ellipsoidal mirror into substantially parallel lightrays, thus making it possible to reduce the size of the first lensarray.

The light 9 leaving the first lens array 4 enters an increasedreflection silver mirror 10 constituting a first reflection mirror, asecond lens array 11 and a first dichroic mirror 12 for reflecting the Bcolor light and transmitting the G and R color light 14, so that the Bcolor light 13 is reflected and the G and R color light 14 aretransmitted. The B color light 13 is reflected from an increasedreflection aluminum mirror 15 constituting a second reflection mirror,and enters a B color light liquid crystal panel 18 constituting a firsttransmission liquid crystal panel through a condenser lens 16 and apolarizing plate 17. The G and R color light 14 enter a second dichroicmirror 19 for reflecting the G color light and transmitting the R colorlight, in which the G color light 20 is reflected and the R color light21 is transmitted. The G color light 20 enters a G color light liquidcrystal panel 24 making up a second transmission liquid crystal panelthrough a condenser lens 22 and a polarizing plate 23.

The R color light 21 enters a R color light liquid crystal panel 31making up a third transmission liquid crystal panel through a relay lens25, a cold mirror 26 constituting a third reflection mirror fortransmitting the infrared light, a relay lens 27, an increasedreflection silver mirror 28 constituting a fourth reflection mirror, acondenser lens 29 and a polarizing plate 30.

The B transmitted light 32 from the liquid crystal panel 18, the Gtransmitted light 33 from the liquid crystal panel 24 and the Rtransmitted light 34 from the liquid crystal panel 31 are synthesized incolor by a dichroic prism 35. The outgoing light 36 thus synthesized incolor is projected on a screen (not shown) by a projection lens 37.

In order to prevent the heat generated from the light source heated to ahigh temperature from having an effect on the component parts other thanthe light source, an exhaust fan 38 for cooling the light source isarranged in the neighborhood of the metal halide lamp 1, the lampreflector 3 and the lamp reflector 5 thereby to exhaust the hot air 39out of the housing of the liquid crystal projector.

The exhaust fan 38 is arranged adjacently to the projection lens 37 andtilted in order to keep the exhaust air 39 of the exhaust fan 38 farfrom the projected light 36 of the projection lens 37. The angle a ofthe portion 36 a of the projected light 36 near to the exhaust air 39 isset to 30°, while the tilt angle b of the exhaust fan is set to 15°, sothat the hot air 39 exhausted from the exhaust fan 38 is prevented fromflowing into the projected light 36 of the projection lens 37. Thus thefluctuations of the image projected on the screen can be lessened.

Also, the exhaust fan 38 is arranged adjacently to the projection lens37, and a plurality of tilted wind-directing plates 40 are arranged insuch positions as to keep the exhaust air 39 of the exhaust fan 38 farfrom the projected light 36 of the projection lens 37. At the same time,the tilt angle c of the wind-directing plate 40 a near to the projectionlens 37 is set larger than the tilt angle d of the wind-directing plate40 b far from the projection lens 37. For example, the tilt angle c isset to 30°, and the tilt angle d is set to 15°. The tilt angle a of theportion 36 a of the projected light 36 near to the exhaust air 39 andthe tilt angle c of the wind-directing plate 40 a near to the projectionlens 37 are both set to the substantially same angle of 30°. Then, thehot air 39 a discharged from the exhaust fan 38 is prevented fromflowing into the projected light 36 from the projection lens 37 and thusthe fluctuations of the image projected on the screen are reduced. Also,in the case where the tilt angle b of the exhaust fan 38 and the tiltangle d of the wind-directing plate 40 b far from the projection lens 37are set to the substantially same 15°, on the other hand, the path ofthe hot air 39 is prevented from being changed considerably by thewind-directing plate 40 b, with the result that the hot air can beexhausted more efficiently. The exhaust air 39 b far from the projectionlens 37 has a smaller effect than the exhaust air 39 a near to theprojection lens 37 on the fluctuations of the image projected on thescreen caused by the hot air 39 exhausted from the exhaust fan 38 andflowing into the projected light 36 of the projection lens 37. Thewind-directing plate 40 b can thus be set to a tilt angle d smaller thanthe tilt angle c of the wind-directing plate 40 a.

According to this embodiment, the first reflection mirror 10, the secondlens array 11, the first dichroic mirror 12, the second dichroic mirror19 and the third reflection mirror 26 are arranged in that order whileat the same time arranging the first reflection mirror 10, the firstlens array 4, the metal halide lamp 4 making up the light source and theexhaust fan 38 in that order so that the first outgoing light 13separated by the first dichroic mirror 12 may constitute the lightreflected from the first dichroic mirror 12 and so that the secondoutgoing light 14 separated by the first dichroic mirror 12 mayconstitute the light transmitted through the first dichroic mirror 12.At the same time, the arrangement of the first reflection mirror 10, thefirst lens array 4, the metal halide lamp 1 making up the light sourceand the exhaust fan 38 is substantially parallel and adjacent to thearrangement of the projection lens 37, the dichroic prism 35 and thesecond dichroic mirror 19.

In the liquid crystal projector having the above-mentioned configurationaccording to this embodiment, the hot air 39 exhausted by the exhaustfan 38 flows in the same direction as the light 36 outgoing from theprojection lens 37. If viewers are located in the neighborhood along thedirection of the light 36 outgoing from the projection lens 37, theoutgoing light 36 would be intercepted by the viewers, therebygenerating their shadow in the image on the screen. In view of the factthat the hot air is prevented from flowing toward the viewers in theneighborhood of the liquid crystal projector, however, the viewers feelno discomfort.

For the same reason, the video equipment such as the personal computerliable to easily succumb to the hot air, which may be located in theneighborhood of the liquid crystal projector, is not exposed to the hotair. Thus there is no need to take the position of the equipment intoconsideration. Also, care need not be taken not to place any objectforming a stumbling block in the path of the hot air in order to exhaustthe heat generated from the light source efficiently. In this way, thepresent invention can improve the operating convenience of theequipment.

Also, according to the present embodiment, the first dichroic mirror 12has such a spectral characteristic as to reflect the B color light andtransmit the G and R color light, and the second dichroic mirror 19 hassuch a spectral characteristic as to reflect the G color light andtransmit the R color light. The B color light component can therefore beincreased as compared with the R color light component. This is byreason of the fact that the mirrors 10, 12 and 15 can be used to reflectonly the B color light, and the S polarized component higher inreflectance than the P polarized component can be utilized. As a result,the white color projected on the screen can be improved to a preferablecolor temperature. Especially, some glass or plastic materials used foroptical parts (such as the polarizing plate and the liquid crystalpanel) of the liquid crystal projector reduce the light utilization rateof the B color light. Therefore, even the use of a light source of thesame color temperature has so far been unable to prevent the reductionin color temperature. The above-mentioned configuration, in contrast,can make the most of the B color light component and therefore canminimize the reduction in color temperature.

Further, according to this embodiment, the first reflection mirror isconfigured of the increased reflection silver mirror 10, the thirdreflection mirror is configured of the cold mirror 26 for transmittingthe infrared light and the fourth reflection mirror is configured of theincreased reflection silver mirror 28 in order to prevent the reductionin the R color light which otherwise might be caused by the extraneoususe of the relay lenses 25, 27 and the reflection mirrors 26, 28.

FIG. 2 is a graph showing the spectral reflectance characteristic of theincreased reflection silver mirror, and FIG. 3 is a graph showing thespectral transmittance of the cold mirror. From these diagrams, theincreased reflection silver mirror is seen to have a higher reflectancethan the cold mirror. Especially, the P polarized component higher intransmittance than the S polarized component should be used for the Rcolor light which uses the light transmitted through the dichroicmirrors 12, 19. The use of the increased reflection silver mirrors 10,28 higher in the reflectance for the P polarized component, therefore,can minimize the reduction in the R color light. In the case where theincreased reflection silver mirrors 10, 28 are used, however, theunnecessary infrared light and ultraviolet light are required to be cutoff. According to this embodiment, the third reflection mirror isconfigured of the cold mirror 26 which transmits the infrared light.Consequently, the harmful infrared light is not irradiated on thepolarizing plate 30 and the liquid crystal panel 31.

Furthermore, according to this embodiment, a UV cut filter forintercepting the ultraviolet light is arranged in the light path betweenthe first dichoric mirror 12 and the polarizing plate 17 arranged on theincidence side of the first liquid crystal panel 18. In fact, thepresent embodiment includes a UV cut filter 17 a formed on the incidentsurface of the polarizing plate 17.

The scope of the present invention is not limited to the configurationaccording to the first embodiment, in which in order to keep the exhaustair 39 of the exhaust fan 38 far from the projected light 36 of theprojection lens 37, the exhaust fan 38 and a plurality of thewind-directing plates 40 are tilted and the tilt angle c of thewind-directing plate 40 a near to the projection lens 37 is set largerthan the tilt angle d of the wind-directing plate 40 b far from theprojection lens 37.

FIG. 4 is a diagram showing a second embodiment of the invention and isa top plan view of an optical system of a liquid crystal projector. Thisembodiment has the same configuration as the first embodiment exceptthat in this embodiment, the exhaust fan 38 is not tilted and thewind-directing plates 40 are not shown. In this embodiment, like in thefirst embodiment, the hot air 39 exhausted from the exhaust fan 38 isprevented from flowing toward the viewers situated in the neighborhoodof the liquid crystal projector, and care need not be exercised to takeinto consideration the position of the equipment which easily succumb tothe heat in the neighborhood of the liquid crystal projector. Nor is itnecessary to take care not to locate any object constituting a stumblingblock to the flow of the hot air exhausted. The present invention is notlimited to the second embodiment in which the portion of the first lensarray near to the light source is formed of a concave lens.Alternatively, various configurations are possible in which thereflector 3 can be an ellipsoidal mirror and a concave lens can beinterposed between the reflector 3 and the second lens array 11, forexample.

FIG. 5 is a diagram showing a third embodiment of the invention and is atop plan view of an optical system of a liquid crystal projector. Theillumination light 51 from a metal halide lamp 50 constituting a lightsource enters a lamp reflector 52 of a parabolic mirror, a UV-IR cutfilter 53, a first lens array 54, a cold mirror 55 constituting a firstreflection mirror, a second lens array 56, and a first dichroic mirrorfor reflecting the R color light and transmitting the G and B colorlight. Thus, the R color light 58 is reflected and the G and B colorlight 59 is transmitted. The R color light 58 is reflected from anincreased reflection aluminum mirror 60 constituting a second reflectionmirror, and enters a R color light liquid crystal panel 63 constitutinga first transmission liquid crystal panel through a condenser lens 61and a polarizing plate 62. The G and B color light 59, on the otherhand, enters a second dichroic mirror 64 for reflecting the G colorlight and transmitting the B color light, so that the G color light 65is reflected and the B color light 66 is transmitted. The G color light65 enters a G color light liquid crystal panel 69 constituting a secondtransmission liquid crystal panel through a condenser lens 67 and apolarizing plate 68. The B color light 66 enters a B color liquidcrystal panel 76 constituting a third transmission liquid crystal panelthrough a relay lens 70, an increased reflection aluminum mirror 71constituting a third reflection mirror, a relay lens 72, an increasedreflection aluminum mirror 73 constituting a fourth reflection mirror, acondenser lens 74 and a polarizing plate 75. The R transmitted light 77from the liquid crystal panel 63, the G transmitted light 78 from theliquid crystal panel 69 and the B transmitted light 79 from the liquidcrystal panel 76 are synthesized in color by a dichroic prism 80. Theoutgoing light 81 thus synthesized in color is projected on a screen(not shown) by a projection lens 82.

In order to eliminate the effect that the heat generated from thehigh-temperature light source otherwise might have on the componentparts other than the light source, a exhaust fan 38 for cooling thelight source is arranged in the neighborhood of the metal halide lamp 50constituting a light source and the lamp reflector 52. The hot air 39thus is exhausted out of the housing (not shown) of the liquid crystalprojector.

According to this embodiment, the first reflection mirror 55, the secondlens array 56, the first dichroic mirror 40, the second dichroic mirror64 and the third reflection mirror 71 are arranged in that order whileat the same time arranging the first reflection mirror 55, the firstlens array 54, the halide lamp 50 making up the light source and theexhaust fan 38 in that order, in order that the first outgoing light 58separated by the first dichroic mirror 40 is reflected from the firstdichroic mirror 40 and the second outgoing light 59 separated by thefirst dichroic mirror 40 is transmitted through the first dichroicmirror 40. At the same time, the arrangement of the first reflectionmirror 55, the first lens array 54, the metal halide lamp 50constituting the light source and the exhaust fan 38 is substantiallyparallel and adjacent to the arrangement of the projection lens 82, thedichroic prism 80 and the second dichroic mirror 64.

The above-mentioned configuration according to the third embodimentcauses the hot air 39 emitted by the exhaust fan 38 to flow in the samedirection as the outgoing light 81 of the projection lens 82, andtherefore has an effect equivalent to that of the second embodiment.

FIG. 6 is a diagram showing light rays from the second lens array 4 tothe projection lens aperture 92 for a liquid crystal panel 85 withmicro-lenses employed according to this invention. Even in the casewhere the outgoing angle g of the liquid crystal panel 18 is increasedby an amount equivalent to the divergence angle e described withreference to FIG. 10, the fact remains that the incident angle f can bereduced by reducing the size of the second lens array 4, and thereforethe light utilization rate can be sufficiently improved without causingany eclipse in the projection lens aperture 92.

FIG. 7 is a top plan view of an optical system of a liquid crystalprojector according to a fourth embodiment of the invention. Thisembodiment is different from the second embodiment in that in thisembodiment, a flat concave lens 43 having a flat surface 42 near to thereflector 3 is interposed between the reflector 3 and the first lensarray 41, and the first lens array 41 is configured of a flat convexlens. According to this embodiment, the aberration performance of thelenses can be improved so that the eclipse in the lens array 11 isminimized for a further improved light utilization rate.

FIG. 8 is a top plan view of an optical system of a liquid crystalprojector according to a fifth embodiment of the invention.

This embodiment is different from the second embodiment in that theportion of the first lens array 44 near to the second lens array 11 isconfigured of a concave lens 45. According to this embodiment, theaperture of the convex lens of the first lens array 44 is required to besomewhat reshaped from a rectangle. In spite of this requirement, theaberration performance of the lenses can be improved over the firstembodiment, and therefore the eclipse in the lens array 11 is reducedfor a further improved light utilization rate.

As described above, according to the present invention, the exhaust fanis arranged adjacently to the projection lens and tilted for the purposeof keeping the exhaust air of the exhaust fan far from the projectedlight. As a result, the hot air emitted from the exhaust fan isprevented from flowing toward the viewers situated in the neighborhoodof the liquid crystal projector, and therefore the viewers feel nodiscomfort. Also, no care need be taken as to the position of theequipment which easily succumb to the heat in the neighborhood of theliquid crystal projector. Nor is it necessary to exercise care not toplace any object forming a stumbling block to the exhaust hot air. Inthis way, the present invention improves the operating convenience whileat the same time eliminating the fluctuations of the screen image sincethe hot air exhausted from the exhaust fan can be prevented from flowinginto the projected light from the projection lens. Also, in thisconfiguration, a plurality of wind-directing plates are arranged tiltedin order to keep the exhaust air of the exhaust fan far from theprojected light of the projection lens, and the tilt angle of thewind-directing plate nearer to the projection lens is set larger thanthe tilt angle of the wind-directing plate far from the projection lens,thereby facilitating the achievement of the above-mentioned variouseffects.

Further, according to the present invention, the first reflectionmirror, the second lens array, the first dichroic mirror, the seconddichroic mirror and the third reflection mirror are arranged in thatorder while at the same time arranging the first reflection mirror, thefirst lens array, the light source and the exhaust fan in that order, inorder that the first outgoing light separated by the first dichroicmirror may be reflected from the first dichroic mirror and the secondoutgoing light separated by the first dichroic mirror may be transmittedthrough the first dichroic mirror. In addition, the arrangement of thefirst reflection mirror, the first lens array, the light source and theexhaust fan is substantially parallel and adjacent to the arrangement ofthe projection lens, the dichroic prism and the second dichroic mirror.The hot air exhausted from the exhaust fan, therefore, is prevented fromflowing toward the viewers situated in the neighborhood of the liquidcrystal projector, and the viewers thus feel no discomfort. Also, nocare need be taken for the layout of the equipment easily succumbing toheat in the neighborhood of the liquid crystal projector, nor is itnecessary to take care not to place any object forming a stumbling blockto the exhaust path of the hot air, thus improving the operatingconvenience.

Further, according to this invention, the provision of a reflector as anellipsoidal mirror and a concave lens interposed between the reflectorand the second lens array can provide the function of converting theconvergent light rays from the reflector into substantially parallellight rays. The first lens array and the second lens array can thus bereduced in size. As a consequence, even in the case where a liquidcrystal panel with micro-lenses is employed, the light utilization ratecan be sufficiently improved.

Since certain changes may be made in the above-mentioned liquid crystalprojector without departing from the spirit and features of theinvention herein involved, it is intended that all matter contained inthe above description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense. The scope ofthe invention is indicated by the claims thereof. Modifications andchanges within the scope of the claims are all included in the scope ofthe invention.

What is claimed is:
 1. A projector which forms an image by irradiatingan illumination light from a light source on a display panel,comprising: a projection lens for projecting the light outgoing fromsaid display panel on a screen; an exhaust fan arranged adjacent to saidprojection lens for exhausting the internal air of said projector tooutside, said exhaust fan being tilted at an angle to the optical axisof said projection lens in such a manner as to direct the exhaust air ofsaid exhaust fan away from the light projected from said projectionlens; wherein said exhaust fan is disposed on a same surface of saidprojector as said projection lens is positioned.
 2. A projector whichforms an image by irradiating an illumination light from a light sourceon a display panel, comprising: a projection lens for protecting thelight outgoing from said display panel on a screen; an exhaust fanarranged adjacent to said projection lens for exhausting the internalair of said projector to outside, wherein said exhaust fan is disposedon a same surface of said projector as said projection lens ispositioned; and a plurality of wind-directing plates arranged at anangle to the optical axis of said projection lens in such a manner thatthe exhaust air of said exhaust fan is directed away from the lightprojected by said projection lens.
 3. A projector which forms an imageby irradiating an illumination light from a light source on a displaypanel, comprising: a projection lens for projecting the light outgoingfrom said display panel on a screen; an exhaust fan for exhausting theinternal air of said projector to outside; and a plurality ofwind-directing plates arranged at an angle to the optical axis of saidprojection lens in such a manner that the exhaust air of said exhaustfan is directed away from the light projected by said projection lens,and the angle of the wind-directing plate nearer to said projection lensis larger than the angle of said wind-directing plate farther away fromsaid projection lens.
 4. A projector which forms an image by irradiatingan illumination light from a light source on a display panel,comprising: a projection lens for projecting the light outgoing fromsaid display panel on a screen; an exhaust fan for exhausting theinternal air of said projector to outside; and a plurality ofwind-directing plates arranged at an angle to the optical axis of saidprojection lens in such a manner that the exhaust air of said exhaustfan is directed away from the light projected by said projection lens,and the angle of the wind-directing plate nearer to said projection lensis larger than the angle of said wind-directing plate farther away fromsaid projection lens.
 5. A projector which forms an image by irradiatingan illumination light from a light source on a display panel,comprising: a projection lens for projecting the light outgoing fromsaid display panel on a screen; an exhaust fan arranged adjacent to saidprojection lens for exhausting the internal air of said projector tooutside, said exhaust fan being tilted at an angle to the optical axisof said projection lens in such a manner as to direct the exhaust air ofsaid exhaust fan away from the projected light of said projection lens,wherein said exhaust fan is disposed on a same surface of said projectoras said projection lens is positioned; and a plurality of wind-directingplates arranged at an angle to the optical axis of said projection lensin such a manner that said exhaust air of said exhaust fan is directedaway from the light projected by said projection lens.
 6. A projectorwhich forms an image by irradiating an illumination light from a lightsource on a display panel, comprising: a projection lens for projectingthe light outgoing from said display panel on a screen; an exhaust fanarranged adjacent to said projection lens for exhausting the internalair of said projector to outside, said exhaust fan being tilted at anangle to the optical axis of said projection lens in such a manner as todirect the exhaust air of said exhaust fan away from the projected lightof said projection lens; and a plurality of wind-directing platesarranged at an angle to the optical axis of said projection lens in sucha manner that said exhaust air of said exhaust fan is directed away fromthe light projected by said projection lens, and the angle of thewind-directing plate near to said projection lens is differentiated fromthe angle of said wind-directing plate farther away from said projectionlens.
 7. A liquid crystal projector which forms an image by irradiatingan illumination light from a light source on a display panel,comprising: a projection lens for projecting the light outgoing fromsaid display panel on a screen; an exhaust fan arranged adjacent to saidprojection lens for exhausting the internal air of the projector tooutside, said exhaust fan being tilted at an angle to the optical axisof said projection lens in such a manner as to direct the exhaust air ofsaid exhaust fan away from the projected light of said projection lens;and a plurality of wind-directing plates arranged at an angle to theoptical axis of said projection lens in such a manner that said exhaustair of said exhaust fan is directed away from the light projected bysaid projection lens, and the angle of the wind-directing plate near tosaid projection lens is larger than the angle of said wind-directingplate farther away from said projection lens.